1. Field of the Invention
The present invention relates to a positioning device, and, more particularly, to a suitable positioning device for positioning an exposure substrate, such as a mask, a reticle (original plate), a semiconductor wafer, or a glass substrate, in an exposure apparatus for producing a device such as a semiconductor device or a liquid crystal display device.
2. Description of the Related Art
A positioning device (stage device) for an exposure apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 2001-230177. In this document, a wafer is placed on a top plate of a stage through a wafer chuck, and an XY slider on which the top plate of the stage is mounted is moved in an X direction and a Y direction by an X guide and a Y guide, respectively. Here, the X guide and the Y guide are driven by linear motors. An electromagnetic coupling and a plurality of linear motors are disposed between the top plate of the stage and the XY slider. The electromagnetic coupling transmits the motion of the XY slider to the top plate of the stage. The linear motors drive the top plate of the stage with respect to the XY slider. The linear motors can drive the top plate of the stage in six axial directions, that is, an X direction, a Y direction, a Z direction, a θx direction (that is, a direction around an X axis), a θy direction (that is, a direction around a Y axis), and a θz direction (that is, a direction around a Z axis). Accordingly, there are six degrees of freedom.
A measuring mirror is disposed on the top plate of the stage. A laser interferometer measures the positions of the top plate of the stage in the six axial directions. A six-degree-of-freedom positional servo system is disposed at the top plate of the stage and acts on the basis of information regarding the measured positions of the top plate in the six axial directions (six-axial-direction positional information). In other words, a command value sent to the linear motors on the back surface of the top plate of the stage is controlled by the calculations of a compensator on the basis of the six-axial direction positional information measured by the laser interferometer.
In recent years, there has been a demand for greater positioning precision and throughput in such a positioning device for an exposure apparatus. In order to meet these demands, it is necessary for the responsiveness of the positional servo system at the stage to be high and for the stage to be capable of moving at a high speed. However, there is a limit as to how high the gain of the positional servo system can be set due to oscillation of the positional servo system. There are various factors that limit servo bandwidth, one of which is vibration in an elastic mode of an object to be controlled.